Silicone composition and method for manufacturing heat-conductive silicone composition

ABSTRACT

A silicone composition that contains an organopolysiloxane having at least two aliphatic unsaturated hydrocarbon groups per molecule, a filler containing an aluminum powder and a zinc oxide powder, an organohydrogenpolysiloxane having two or more SiH groups per molecule, and a platinum group metal catalyst, in which when a storage and loss elastic modulus G″ of the silicone composition is measured by means a viscoelasticity measurement apparatus capable of measuring shear modulus, the silicone composition can provide a cured product wherein G′ after 3,000 seconds from the start of holding is 10,000 Pa or less, G′ after 7,200 seconds from the start of holding is 100,000 Pa or less, and G′ exceeds G″ after 800 seconds or more from the start of holding. As a result, there is provided a silicone composition excellent in crushability, spreadability, and heat conductivity.

This is a Continuation of application Ser. No. 14/914,100 filed Feb. 24,2016, which in turn is a National Stage of PCT ApplicationPCT/JP2014/003157, filed Jun. 13, 2014, which claims priority to JP2013-194880, filed Sep. 20, 2013. The disclosure of the priorapplications is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to a silicone composition and a method formanufacturing a heat-conductive silicone composition.

BACKGROUND ART

It is widely known that electronic parts such as semiconductor packagesgenerate heat in use, thereby lowering the performance thereof. To solvethis problem, various heat dissipating techniques have been used. Onetypical method is to provide a cooling member such as a heat spreader inthe vicinity of a heat-generating part and bring them into close contactto effectively remove heat through the cooling member.

In this case, if there is a space between the heat-generating member andthe cooling member, thermal conduction does not proceed smoothly becauseof the presence of air, which is poor in heat conductivity, andtherefore, the temperature of the heat-generating member cannot besufficiently reduced. To prevent such phenomena, there have beenconventionally used, for the purpose of preventing the presence of air,heat-dissipating greases or heat-dissipating sheets that have good heatconductivity and followability to the surface of the member (PatentLiteratures 1 to 11).

A thin and compressible heat-dissipating grease is suitable for measuresagainst heat of semiconductor packages in view of heat-dissipatingperformance. Particularly, it is preferable, in view of reliability, touse a thermosetting heat-dissipating grease that hardly causes outflowof the grease (pumping out) due to the thermal history between heatingand cooling of the heat-generating part. In general, a thermosettingheat-dissipating grease contains a reaction retarder in many cases, sothat the grease is not cured for a certain time at room temperature evenafter applied to a heat-generating part. Accordingly, even if a certaintime passes after the heat-dissipating grease is applied, theheat-dissipating grease can be compressed and thermally cured into adesired thickness after a cooling member such as a heat spreader isplaced thereon, and thus, good crushability can be achieved.

On the other hand, semiconductor packages progress towardminiaturization in recent years, and along with this current,application to finer pattern and less application amount are required inheat-dissipating greases. In these cases, the reaction retarder tends tovolatilize due to the increase in surface area of the appliedheat-dissipating grease or other factors, which leads to acceleration ofthe curing reaction. Therefore, the heat-dissipating grease cannot becompressed into a desired thickness when the heat-dissipating grease isthermally cured after a cooling member such as a heat spreader is placedthereon, that is, resulting poor crushability. In addition, the appliedheat-dissipating grease cannot sufficiently spread over the wholeheat-generating part. Thus, there is a problem of insufficientheat-dissipating performance,

CITATION LIST Patent Literature

PATENT LITERATURE 1: Japanese Patent No. 2938428

PATENT LITERATURE 2: Japanese Patent No. 2938429

PATENT LITERATURE 3: Japanese Patent No. 3580366

PATENT LITERATURE 4: Japanese Patent No. 3552184

PATENT LITERATURE 5: Japanese Patent No. 4572243

PATENT LITERATURE 6: Japanese Patent No. 4656340

PATENT LITERATURE 7: Japanese Patent No. 4913874

PATENT LITERATURE 8: Japanese Patent No. 4917380

PATENT LITERATURE 9: Japanese Patent No. 4933094

PATENT LITERATURE 10: Japanese Unexamined Patent publication (Kokai) No.2012-102283

PATENT LITERATURE 11: Japanese Unexamined Patent publication (Kokai) No.2012-96361

SUMMARY OF INVENTION Technical Problem

The present invention was accomplished in view of the above-describedproblems. It is an object of the present invention to provide a siliconecomposition excellent in crushability, spreadability, and heatconductivity, and further provide a method for manufacturing aheat-conductive silicone composition.

Solution to Problem

To achieve this object, the present invention provides a siliconecomposition comprising: (A) 100 parts by mass of an organopolysiloxanehaving at least two aliphatic unsaturated hydrocarbon groups permolecule, and having a kinematic viscosity at 25° C. of 60 to 100,000mm²/s; (B) 100 to 2,000 parts by mass of a filler containing an aluminumpowder and a zinc oxide powder; (C) an organohydrogenpolysiloxane havingtwo or more silicon-bonded hydrogen atoms (i.e. SiH group) per molecule,in such an amount that a ratio of a number of the SiH groups in thecomponent (C) to a total number of the aliphatic unsaturated hydrocarbongroups in the component (A) ranges from 0.5 to 1.5; and (D) a platinumgroup metal catalyst in an amount of 0.1 to 500 ppm in terms of platinumwith respect to the component wherein when a storage elastic modulus G′and a loss elastic modulus G″ of the silicone composition is measured,by means of a viscoelasticity measurement apparatus capable of measuringshear modulus, while holding the silicone composition at 150° C. for7,200 seconds after the silicone composition is heated from 25° C. to125° C. at a temperature increase rate of 10° C./min, from 125° C. to145° C. at a temperature increase rate of 2° C./min, and from 145° C. to150° C. at a temperature increase rate of 0.5° C./min, the siliconecomposition can provide a cured product in which the storage elasticmodulus G′ after 3,000 seconds from the start of holding is 10,0001 Paor less, the storage elastic modulus G′ after 7,200 seconds from thestart of holding is 100,000 Pa or less, and the storage elastic modulusG′ exceeds the loss elastic modulus G″ after 800 seconds or more fromthe start of holding.

Such a silicone composition enables a heat-dissipating grease formedfrom the composition to be compressed into a desired thickness when theheat-dissipating grease is thermally cured after a cooling member suchas a heat spreader is placed thereon even in the case that theheat-dissipating grease is applied to a fine pattern and/or with alittle amount, and also enables the applied heat-dissipating grease tosufficiently spread over the whole heat-generating part. Therefore,sufficient heat-dissipating performance can be obtained.

The silicone composition preferably further comprise (E) 1 to 200 partsby mass of a hydrolytic methylpolysiloxane represented by the generalformula (1), based on 100 parts by mass of the component (A),

wherein R¹ represents an alkyl group having 1 to 6 carbon atoms; and “a”is an integer of 5 to 100.

When such a hydrolytic methylpolysiloxane is contained, sufficientwettability can be exhibited, and curing reaction progressessufficiently, whereby outflow of the grease can be prevented.

The silicone composition preferably further comprises (F) 0.05 to 1.0part by mass of one or more retarders selected from the group consistingof acetylene compounds, nitrogen compounds, organophosphorous compounds,oxime compounds, and organochlorine compounds, based on 100 parts bymass of the component (A).

When the component (F) is contained, it functions as a retarder andsuppresses progress of the hydrosilylation reaction at room temperature,whereby the shelf life or the pot life can be extended.

In addition, the present invention provides a heat-dissipating greaseobtained by curing the silicone composition of the present invention.

Since the silicone composition of the present invention is excellent incrushability, spreadability, and heat conductivity, the heat-dissipatinggrease which is a cured product of the silicone composition hasexcellent heat conductivity and quality characteristics.

Further, the present invention provides a method for manufacturing aheat-conductive silicone composition, comprising the steps of: producinga silicone composition containing (A) 100 parts by mass of anorganopolysiloxane having at least two aliphatic unsaturated hydrocarbongroups per molecule, and having a kinematic viscosity at 25° C. of 60 to100,000 mm²/s, (B) 100 to 2,000 parts by mass of a filler containing analuminum powder and a zinc oxide powder, (C) anorganohydrogenpolysiloxane having two or more silicon-bonded hydrogenatoms (i.e. SiH group) per molecule, in such an amount that a ratio of anumber of the SiH groups in the component (C) to a total number of thealiphatic unsaturated hydrocarbon groups in the component (A) rangesfrom 0.5 to 1.5, and (D) a platinum group metal catalyst in an amount of0.1 to 500 ppm in terms of platinum with respect to the component (A);measuring a storage elastic modulus G′ and a loss elastic modulus G″ ofthe silicone composition, by means of a viscoelasticity measurementapparatus capable of measuring shear modulus, while holding the siliconecomposition at 150° C. for 7,200 seconds after the silicone compositionis heated from 25° C. to 125° C. at a temperature increase rate of 10°C./min, from 125° C. to 145° C. at a temperature increase rate of 2°C./min, and from 145° C. to 150° C. at a temperature increase rate of0.5° C./min; and selecting a heat-conductive silicone composition thatcan provide a cured product in which the storage elastic modulus G′after 3,000 seconds from the start of holding is 10,000 Pa or less, thestorage elastic modulus G′ after 7,200 seconds from the start of holdingis 100,000 Pa or less, and the storage elastic modulus exceeds the losselastic modulus G″ after 800 seconds or more from the start of holding.

In this way, when the method for manufacturing a heat-conductivesilicone composition including selecting a silicone compositionsatisfying the desired requirements is employed, a heat-conductivesilicone composition having excellent crushability and spreadability canbe stably obtained.

Advantageous Effects Invention

The silicone composition of the present invention is excellent in heatconductivity, and even in the case that a heat-dissipating grease formedfrom the composition is applied to a fine pattern and/or with a littleamount, the heat-dissipating grease can be compressed into a desiredthickness when the heat-dissipating grease is thermally cured after acooling member such as a heat spreader is placed thereon; and inaddition, the applied heat-dissipating grease can sufficiently spreadover the whole heat-generating part. Therefore, sufficientheat-dissipating performance can be obtained. Further, when the methodfor manufacturing a heat-conductive silicone composition of the presentinvention is employed, a heat-conductive silicone composition havingexcellent crushability and spreadability can be surely obtained.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in More detail.

As described above, it has been desired to develop a siliconecomposition in which, even in the case that the composition is appliedto a fine pattern and/or with a little amount as a heat-dissipatinggrease, the heat-dissipating grease can be compressed into a desiredthickness when the heat-dissipating grease is thermally cured after acooling member such as a heat spreader is placed thereon, and theapplied heat-dissipating grease can sufficiently spread over the wholeheat-generating part.

The present inventors diligently studied to achieve the above object,and consequently found that the silicone composition containing thecomponents (A) to (D) and optionally containing the components (E) and(F), in which the composition satisfies the specific requirements of thestorage elastic modulus G′ and the time necessary for the storageelastic modulus G′ to exceed the loss elastic modulus G″ when thestorage elastic modulus G′ and the loss elastic modulus G″ of thesilicone composition is measured by a viscoelasticity measurementapparatus capable of measuring shear modulus, enables a heat-dissipatinggrease formed from the composition to be compressed into a desiredthickness when the heat-dissipating grease is thermally cured after acooling member such as a heat spreader is placed thereon even in thecase that the heat-dissipating grease is applied to a fine patternand/or with a little amount, and also enables the appliedheat-dissipating grease to sufficiently spread over the wholeheat-generating part, so that sufficient heat-dissipating performancecan be obtained, thereby brought the present invention to completion.

Hereinafter, the silicone composition of the present invention will bedescribed in detail, but the present invention is not limited thereto.

The silicone composition of the present invention contains (A) 100 partsby mass of an organopolysiloxane having at least two aliphaticunsaturated hydrocarbon groups per molecule, and having a kinematicviscosity at 25° C. of 60 to 100,000 mm²/s; (B) 100 to 2,000 parts bymass of a filler containing an aluminum powder and a zinc oxide powder;(C) an organohydrogenpolysiloxane having two or more silicon-bondedhydrogen atoms (i.e. SiH group) per molecule, in such an amount that aratio of a number of the SiH groups in the component (C) to a totalnumber of the aliphatic unsaturated hydrocarbon groups in the component(A) ranges from 0.5 to 1.5; and (D) a platinum group metal catalyst inan amount of 0.1 to 500 ppm in terms of platinum with respect to thecomponent (A); and when a storage elastic modulus G′ and a loss elasticmodulus G″ of the silicone composition is measured, by means of aviscoelasticity measurement apparatus capable of measuring shearmodulus, while holding the silicone composition at 150° C. for 7,200seconds after the silicone composition is heated from 25° C. to 125° C.at a temperature increase rate of 10° C./min, from 125° C. to 145° C. ata temperature increase rate of 2° C./min, and from 145° C. to 150° C. ata temperature increase rate of 0.5° C./min, the silicone composition canprovide a cured product in which the storage elastic modulus G′ after3,000 seconds from the start of holding is 10,000 Pa or less, thestorage elastic modulus G′ after 7,200 seconds from the start of holdingis 100,000 Pa or less, and the storage elastic modulus G′ exceeds theloss elastic modulus G″ after 800 seconds or more from the start ofholding.

When the storage elastic modulus G′ and the loss elastic modulus G″ ofthe silicone composition is measured by means of a viscoelasticitymeasurement apparatus capable of measuring shear modulus under the abovetemperature increase conditions and high-temperature holding condition,if the storage elastic modulus G′ after 3,000 seconds from the start ofholding exceeds 10,000 Pa, or the storage elastic modulus G′ after 7,200seconds from the start of holding exceeds 100,000 Pa, or the storageelastic modulus G′ exceeds the loss elastic modulus G″ in less than 800seconds from the start of holding, there is fear that theheat-dissipating grease formed from the composition cannot be compressedinto a desired thickness when the heat-dissipating grease is thermallycured after a cooling member such as a heat spreader is placed thereonin the case that the heat-dissipating grease is applied to a finepattern and/or with a little amount, and that the appliedheat-dissipating grease cannot sufficiently spread over the wholeheat-generating part.

Hereinafter, each component constituting the silicone composition of thepresent invention will be described in more detail.

[Component (A)]

The component (A) is an organopolysiloxane having at least two aliphaticunsaturated hydrocarbon groups per molecule, and having a kinematicviscosity at 25° C. of 60 to 100,000 mm²/s. The aliphatic unsaturatedhydrocarbon group is preferably a monovalent hydrocarbon groupcontaining aliphatic unsaturated bond and having 2 to 8 carbon atoms,more preferably 2 to 6 carbon atoms, and it is much more preferably analkenyl group. Examples thereof include alkenyl groups such as a vinylgroup, an allyl group, a propenyl group, an isopropenyl group, a butenylgroup, a hexenyl group, a cyclohexenyl group, and an octenyl group. Avinyl group is particularly preferred. The aliphatic unsaturatedhydrocarbon group may be bonded to either silicon atoms in terminals ofthe molecular chain or silicon atoms within the molecular chain, or maybe bonded to both of them.

The organopolysiloxane has a kinematic viscosity at 25° C. of 60 to100,000 mm²/s, preferably 100 to 30,000 mm²/s. If the kinematicviscosity less than 60 mm²/s, there is fear that physical properties ofthe silicone composition are lowered, whereas if it exceeds 100,000mm²/s, the silicone composition may become poor in spreadability.

In the present invention, the kinematic viscosity is a value measured byUbbelohde-type Oswald viscometer at 25° C.

The molecular structure of the organopolysiloxane is not particularlylimited so long as it has the above-mentioned properties, and examplesthereof include linear structure, branched structure, and linearstructure having partially branched or cyclic structure. Particularlypreferable is a linear structure in which the main chain is composed ofdiorganosiloxane repeating units and both terminals of the molecularchain are blocked with triorganosiloxy groups. Organopolysiloxane havingsaid linear structure may have a partially branched or cyclic structure.The organopolysiloxane may be used solely or in combination of two ormore kinds.

An organic group bonded to silicon atoms in the organopolysiloxane otherthan the aliphatic unsaturated hydrocarbon group is a substituted orunsubstituted monovalent hydrocarbon group having 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, more preferable 1 to 8 carbon atoms.Examples thereof include alkyl groups such as methyl group, ethyl group,propyl group, isopropyl group, butyl group, isobutyl group, tent-butylgroup, pentyl group, neopentyl group, hexyl group, cyclohexyl group,octyl group, nonyl group, and decyl group; aryl groups such as phenylgroup, tolyl group, xylyl group, and naphthyl group; aralkyl groups suchas benzyl group, phenethyl group, and phenylpropyl group; and groups inwhich a part or whole of hydrogen atoms in these groups are substitutedwith halogen atoms such as fluorine, bromine, and chlorine or cyanogroups, such as chloromethyl group, chloropropyl group, bromoethylgroup, trifluoropropyl group, and cyanoethyl group. Particularly, methylgroup is preferred.

[Component (B)]

The component (B) is a heat-conductive filler containing an aluminumpowder and a zinc oxide powder. In the present invention, the shape ofthe aluminum powder is not particularly limited, and may be spherical,irregular shape, or other shape. The surface of the aluminum powder maybe previously treated. The aluminum powder preferably has an averageparticle size of 0.1 to 100 μm, more preferably 1 to 40 μm. If theaverage particle size of the aluminum powder is 0.1 μm or more,viscosity of the resulting composition is not too high, and thus, thereis no fear that the spreadability thereof becomes poor. If it is 100 μmor less, the resulting composition becomes homogeneous.

In the present invention, as the aluminum powder, an aluminum powderhaving a large average particle size or small average particle size maybe used alone, but it is preferred to mixedly used an aluminum powderhaving a large average particle size (e.g. 5 μm or more and 100 μm orless, preferably 10 μm or more and 100 μm or less, more preferably 10 μmor more and 50 μm or less) and an aluminum powder having a small averageparticle size (e.g. 0.1 μm or more and 10 μm or less, preferably 0.1 μmor more and 5 μm or less, more preferably 1 μm or more and 5 μm orless).

The mixing ratio may be adjusted according to a desired viscosity of thegrease, and it is particularly preferred that the mass ratio of thealuminum powder having a large average particle size to the aluminumpowder having a small average particle size range from 0.5 to 9.0, morepreferably from 1.0 to 5.0. In addition, by using the two aluminumpowders having different particle sizes and the zinc oxide powder as (B)the filler of the silicone composition of the present invention, thecomposition of the present invention exhibits more excellent viscosity.Thus, the grease formed from the composition also exhibits excellentviscosity.

In the present invention, the shape of the zinc oxide powder is notparticularly limited, and may be spherical, irregular shape, or othershape. The zinc oxide powder preferably has an average particle size of0.1 to 10 μm, more preferably 1 to 4 μm. If the average particle size ofthe zinc oxide powder is 0.1 μm or more, there is no fear that theresulting composition exhibits a high viscosity, and that thespreadability thereof becomes poor. If it is 10 μm or less, theresulting composition becomes homogeneous.

In the present invention, the “average particle size” indicates theparticle size of 50% integrated value in the particle size distributionbased on volume measured by a laser diffractive-scattering method. Themeasurement using the laser diffractive-scattering method can beperformed, for example, by a Microtrack particle size analyzer MT3300EX,(manufactured by Nikkiso Co., Ltd.).

In the present invention, (B) the filler may further contain, besidesthe aluminum powder and the zinc oxide powder, a known heat-conductivefiller such as titanium oxide powder, alumina powder, boron nitridepowder, aluminum nitride powder, diamond powder, gold powder, silverpowder, copper powder, carbon powder, nickel powder, indium powder,gallium powder, metallic silicon powder, and silica powder, depending onthe purpose.

The amount of (B) the filler is 100 to 2,000 parts by mass, preferably200 to 1,800 parts by mass, more preferably 400 to 1,800 parts by mass,based on 100 parts by mass of the component (A). If the amount of thefiller is less than 100 parts by mass, the resulting composition maybecome poor in heat conductivity. If the amount exceeds 2,000 parts bymass, the composition may become poor in spreadability.

[Component (C)]

The component (C) is an organohydrogenpolysiloxane having two or more,preferably three or more, particularly preferably 3 to 100, furtherpreferably 3 to 20 silicon-bonded hydrogen atoms (i.e. SiH groups) permolecule. The organohydrogenpolysiloxane may be any materials so long asthe SiH groups in the molecule are subjected to addition reaction withthe aliphatic unsaturated hydrocarbon groups contained in the component(A) in the presence of a later-described platinum group metal catalystto form a crosslinking structure.

The molecular structure of the organohydrogen-polysiloxane is notparticularly limited so long as it has the above-mentioned properties,and examples thereof include linear structure, branched structure,cyclic structure, and linear structure having partially branched orcyclic structure. Particularly preferable is linear or cyclic structure.The organohydrogenpolysiloxane preferably has a kinematic viscosity at25° C. of 1.0 to 1,000 mm²/s, more preferably 10 to 100 mm²/s. If thekinematic viscosity is 1.0 mm²/s or more, there is no fear that physicalproperties of the silicone composition are lowered. If it is 1,000 mm²/sor less, there is no fear that the spreadability of the siliconecomposition becomes poor.

As the organic group bonded to silicon atoms in theorganohydrogenpolysiloxane, there may be mentioned a monovalenthydrocarbon group other than an aliphatic unsaturated hydrocarbon group,in particular, an unsubstituted or substituted monovalent hydrocarbongroup having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms.Examples thereof include alkyl groups such as methyl group, ethyl group,propyl group, butyl group, hexyl group, and dodecyl group; aryl groupssuch as phenyl group; aralkyl groups such as 2-phenethyl group and2-phenylpropyl group; groups in which a part or whole of hydrogen atomsin these groups are substituted with halogen atoms such as fluorine,bromine, and chlorine or cyano groups, such as chloromethyl group,chloropropyl group, bromoethyl group, trifluoropropyl group, andcyanoethyl group; and epoxy ring-containing organic groups (alkyl groupssubstituted with glycidyl group or glycidyloxy group) such as2-glycidoxyethyl group, 3-glycidoxypropyl group, and 4-glycidoxybutylgroup. The organohydrogenpolysiloxane may be used solely or incombination of two or more kinds.

The amount of (C) the organohydrogenpolysiloxane is such an amount thatthe ratio of a number of the SiH groups in the component (C) to a totalnumber of the aliphatic unsaturated hydrocarbon groups in the component(A) is in the range of 0.5 to 1.5, If the amount of the component (C) isless than 0.5, there is fear that the curing reaction does not proceedsufficiently, and thus outflow of the grease occurs. If it exceeds 1.5,unreacted SiH groups may cause excess crosslinking reaction, so that itbecomes difficult to compress the heat-dissipating grease into aprescribed thickness during thermal curing, and to sufficiently spreadthe applied heat-dissipating grease over the whole heat-generating part,which may result in insufficient heat-dissipating performance.

[Component (D)]

The component (D) is a platinum group metal catalyst, which serves toaccelerate the addition reaction mentioned above. As the platinum groupmetal catalyst, conventionally known materials used for additionreaction can be used. Examples thereof include platinum-based,palladium-based, rhodium-based, and ruthenium-based catalyst. Amongthem, platinum and a platinum compound are preferred because ofrelatively high availability thereof. For example, simple platinum,platinum black, chloroplatinic acid, platinum-olefin complexes,platinum-alcohol complexes, and platinum coordination compounds may bementioned. The platinum-based catalyst may be used solely or incombination of two or more kinds.

The amount of the component (D) is 0.1 to 500 ppm, preferably 1.0 to 100ppm in terms of platinum group metal atoms relative to the component (A)on the basis of mass if the amount of the catalyst is less than 0.1 ppm,there is fear that no catalytic effect is expected. If it exceeds 500ppm, the catalytic effect does not increase, resulting in poor economy,so that it is not preferable.

[Component (E)]

The silicone composition of the present invention may further contain ahydrolytic methylpolysiloxane represented by the formula (1).

In the formula (1), R¹ represents an alkyl group having 1 to 6 carbonatoms; and examples thereof include methyl group, ethyl group, propylgroup, isopropyl group, butyl group, sec-butyl group, tert-butyl group,pentyl group, and hexyl group. “a” is an integer of 5 to 100. If thevalue of “a” is 5 or more, oil-bleeding from the silicone compositiondoes not become prominent, and sufficient reliability can be obtained.If the value of “a” is 100 or less, wettability to the filler becomessufficient.

The amount of the component (E) is 1 to 200 parts by mass, preferably 10to 150 parts by mass, more preferably 20 to 100 parts by mass, based on100 parts by mass of the component (A). If the amount of the component(E) is 1 part by mass or more, sufficient wettability can be expressed.If the amount of the component (E) is 200 parts by mass or less, curingreaction proceeds sufficiently, and there is no fear that outflow of thegrease occurs.

[Component (F)]

The silicone composition of the present invention may further containcomponent (F), a retarder. The retarder serves to suppress the progressof the hydrosilylation reaction at room temperature, and is used forextending shelf life or pot life. As the retarder, a conventionallyknown retarder used for an addition-curable silicone composition can beused. Examples thereof include acetylene compounds such as acetylenealcohols (e.g., ethynylmethyldecylcarbinol, 1-ethynyl-1-cyclohexanol and3,5-dimethyl-1-hexyn-3-ol); various nitrogen compounds such astributylamine, tetramethylethylenediamine, and benzotriazol;organophosphorus compounds such as triphenylphosphine; oxime compounds;and organochlorine compounds.

The amount of the component (F) is 0.05 to 1.0 part by mass, preferably0.1 to 1.0 part by mass, based on 100 parts by mass of the component(A). If the amount of the retarder is 0.05 part by mass or more, adesired sufficient shelf life or pot life can be obtained. If it is 1.0part by mass or less, there is no fear that curability of the siliconecomposition is lowered, so that it is preferable.

The retarder may be diluted with organo(poly)siloxane, toluene, or thelike to enhance dispersibility to the silicone composition.

[Other Additives]

The silicone composition of the present invention may contain unreactiveorgano(poly)siloxane such as methylpolysiloxane to adjust elasticity andviscosity of the composition. In addition, to prevent deterioration ofthe silicone composition, a conventionally known antioxidant such as2,6-di-t-butyl-4-methylphenol may be added, if necessary. Further, adye, a pigment, a flame retardant, a precipitation-inhibitor, athixotropy-enhancer, or other additives may be blended, if necessary.

Next, the method for manufacturing a heat-conductive siliconecomposition of the present invention will be described, but it is notlimited thereto.

The method for manufacturing a heat-conductive silicone composition ofthe present invention includes the steps of: producing a siliconecomposition that contains the above components (A) to (D) and, inaddition to these, may further contains components (E) and (F);measuring a storage elastic modulus G′ and a loss elastic modulus G″ ofthe produced silicone composition by means of a viscoelasticitymeasurement apparatus capable of measuring shear modulus under the abovetemperature increase conditions and high-temperature holding condition;and selecting a silicone composition that can provide a cured product inwhich measured values of the storage elastic modulus G′ and the losselastic modulus G″ satisfy the desired requirements.

[Step of Producing Silicone Composition]

A method for producing the silicone composition in the present inventionmay follow the conventional method for producing a silicone greasecomposition, and is not particularly limited. For example, thecomposition can be produced by mixing the components (A) to (F) and anyother optional components with a mixer such as a Trimix, Twinmix orPlanteary Mixer (all registered trademarks for mixers manufactured byInoue Manufacturing Co., Ltd.), an Ultramixer (a registered trademarkfor a mixer manufactured by Mizuho Industrial Co., Ltd.), and a HivisDisper Mix (a registered trademark for a mixer manufactured by PRIMIXCorporation).

The silicone composition of the present invention preferably has aviscosity measured at 25° C. of 3.0 to 300 Pa·s, more preferably 5.0 to200 Pa·s. The viscosity of 3.0 Pa·s or more is preferable because thereis no fear that the workability is lowered. The above viscosity can beachieved by adjusting the composition of the respective components. Inthe present invention, the viscosity is a value measured at 25° C. by aMalcolm viscometer (at 10 rpm with Rotor-A, and at a shear rate of 6[l/s]).

[Step of Measuring Storage Elastic Modulus G′ and Loss Elastic ModulusG″]

The produced silicone composition is heated from 25° C. to 125° C. at atemperature increase rate of 10° C./min, from 125° C. to 145° C. at atemperature increase rate of 2° C./min, and from 145° C. to 150° C. at atemperature increase rate of 0.5° C./min, and then, a storage elasticmodulus G′ and a loss elastic modulus G″ of the silicone composition ismeasured while holding the silicone composition at 150° C. for 7,200seconds, by using a viscoelasticity measurement apparatus capable ofmeasuring shear modulus. As an example of the apparatus used in thisstep, there may be mentioned a viscoelasticity measurement apparatus(Type RDAIII, manufactured by Rheometric Scientific Ltd.).

[Step of Selecting Silicone Composition]

Then, a silicone composition that can provide a cured product in whichthe storage elastic modulus G′ after 3,000 seconds from the start ofholding is 10,000 Pa or less, the storage elastic Modulus G′ after 7,200seconds from the start of holding is 100,000 Pa or less, and the storageelastic modulus G′ exceeds the loss elastic modulus G″ after 800 secondsor more from the start of holding, is selected.

That is, in the manufacturing of a heat-conductive silicone composition,only compositions satisfying the above requirements are selected fromthe produced silicone compositions. As a result, a heat-conductivesilicone composition excellent in crushability and spreadability can besurely obtained.

The silicone composition (heat-conductive silicone composition) of thepresent invention can be suitably used, as well as the conventionalheat-conductive silicone grease, for dissipating heat by placing thecomposition between a cooling member and a heat-generating member suchas electronic parts of a semiconductor package to conduct heat from theheat-generating member to the cooling member. In particular, it iseffective for the case where the heat-dissipating grease is applied to afine pattern and/or with a little amount. The curing conditions when thesilicone composition of the present invention is thermally cured are notparticularly limited, but generally 80 to 200° C., preferably 100 to180° C., for 30 minutes to 4 hours, preferably 30 minutes to 2 hours.

EXAMPLES

Hereinafter, the present invention will be more specifically describedwith reference to examples and comparative examples, but the presentinvention is not limited to the following examples.

Examples 1 to 18 and Comparative examples 1 to 14

The following components (A) to (F) were mixed as described below toobtain compositions of Examples 1 to 18 and Comparative examples 1 to14.

That is, the components (A), (B), and (E) were placed into a 5-LPlanteary Mixer (manufactured by Inoue Manufacturing Co., Ltd.) with theblending ratio shown in Tables 1 to 4, and mixed for 1 hour at 170° C.Then, the components (C), (D), and (F) were added thereto, and mixedhomogeneously.

The respective components used in examples and comparative examples areshown below. In the following, the kinematic viscosity is a valuemeasured by Ubbelohde-type Oswald viscometer (manufactured by Sibatascientific technology Ltd.) at 25° C.

[Component (A)]

A-1: dimethylpolysiloxane having a kinematic viscosity at 25° C. of 600mm²/s in which both terminals are blocked with dimethylvinylsilylgroups.

A-2: dimethylpolysiloxane having a kinematic viscosity at 25° C. of 700mm²/s in which both terminals are blocked with trimethylsilyl groups andtwo of methyl groups bonded to silicon atoms within the molecular chainare vinyl groups.

[Component (B)]

B-1: an aluminum powder having an average particle size of 10.0 μm (heatconductivity: 237 W/m·° C.)

B-2: a zinc oxide powder having an average particle size of 1.0 μm (heatconductivity: 25 W/m·° C.)

[Component (D)]

D-1: a solution in which a platinum-divinyltetramethyldisiloxane complexwas dissolved in the same dimethylpolysiloxane as A-1 (platinum atomcontent: 1% by mass).

The following properties were measured with respect to thesecompositions.

[Storage Elastic Modulus and Time Required for storage Elastic Modulusto Exceed Loss Elastic Modulus]

The silicone composition was applied between two parallel plates eachhaving a diameter of 2.5 cm so as to give a thickness of 2 mm. Then, aprogram was constructed for heating the coated plates from 25° C. to125° C. at a temperature increase rate of 10° C./min, from 125° C. to145° C. at a temperature increase rate of 2° C./min, and from 145° C. to150° C. at a temperature increase rate of 0.5° C./min and then holdingthem at 150° C. for 7,200 seconds. After that, storage elastic modulusafter 3,000 seconds and 7,200 seconds from the start of holding at 150°C. and the time required for the storage elastic modulus to exceed theloss elastic modulus were measured. The measurement was performed usinga viscoelasticity measurement apparatus (Type: RDAIII, manufactured byRheometric Scientific Ltd.).

[Viscosity]

The absolute viscosity of the silicone composition was measured by aMalcolm viscometer (type: PC-1T) at 25° C.

[Heat Conductivity]

The silicone composition was wrapped with kitchen wrap and measured byTPA-501 manufactured by Kyoto electronics manufacturing Co., Ltd.

[Crushability Test]

6 mg of the silicone composition was applied onto a silicon wafer (10mm×10 mm), and left to stand at 25° C. for 4 hours. Thereafter, anothersilicon wafer with the same size was placed thereon, and the compositionwas cured at 150° C. for 2 hours under a pressure of 10 gf. Then, thethickness of the silicone composition was measured.

[Spreadability Test]

The test sample used in the crushability test was separated into twosilicon wafers, and (area covered with the silicone composition)/(areaof the silicon wafer) was calculated.

Measurement results of storage elastic modulus, a time required for thestorage elastic modulus to exceed the loss elastic modulus, viscosity,and heat conductivity, and results of the crushability test and thespreadability test of the obtained compositions were shown in Tables 1to 4. Examples 1 to 18 are shown in Tables 1 and 2, and Comparativeexamples 1 to 14 are shown in Tables 3 and 4. SiH/SiVi (number ratio)indicates the ratio of the number of SiH groups in the components (C) tothe total number of aliphatic unsaturated hydrocarbon groups in thecomponent (A).

TABLE 1 Example Example Example Example Example Example Example ExampleExample 1 2 3 4 5 6 7 8 9 A-1 100 100 100 100 100 100 A-2 100 100 100B-1 814 814 1240 600 1240 600 814 814 814 B-2 100 100 152 74 152 74 100100 100 Total amount of 914 914 1392 674 1392 674 914 914 914 filler C-17.9 7.4 7.9 7.9 7.4 7.4 4.7 4.0 C-2 11.7 C-3 4.6 D-1 0.06 0.06 0.06 0.060.06 0.06 0.06 0.06 0.06 E-1 100 100 100 100 100 100 100 100 100 F-1 0.40.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 SiH/SiVi 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.00.5 (number ratio) Storage elastic 6,450 2,430 7,090 5,840 3,010 2,4002,280 8,380 850 modulus G′ (after 3,000 sec) Storage elastic 46,90041,990 55,020 40,590 48,370 37,220 26,270 38,550 4,690 modulus G′ (after7,200 sec) Time required for 1,620 917 1,300 1,760 856 1,010 2,140 9401,910 storage elastic modulus to exceed loss elastic modulus (sec)Viscosity 9.7 10.0 31 5.0 33 5.5 8.6 9.5 10.1 (Pa · s) Heat conductivity2.0 2.0 3.0 1.1 3.0 1.2 1.9 2.0 2.0 (W/m · ° C.) Thickness of 40 38 4835 47 33 37 43 32 silicone composition after crushability test (μm)Result of 0.71 0.75 0.55 0.86 0.57 0.89 0.78 0.66 0.88 spreadabilitytest (area covered with silicone composition/area of silicon wafer)

TABLE 2 Example Example Example Example Example Example Example ExampleExample 10 11 12 13 14 15 16 17 18 A-1 100 100 100 100 100 100 A-2 100100 100 B-1 814 814 814 814 814 814 814 814 814 B-2 100 100 100 100 100100 100 100 100 Total amount of 914 914 914 914 914 914 914 914 914filler C-1 5.5 7.9 7.4 7.9 7.4 C-2 14.1 17.6 11.7 11.0 C-3 D-1 0.06 0.060.06 0.09 0.09 0.06 0.06 0.06 0.06 E-1 100 100 100 100 100 70 70 100 100F-1 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.6 0.6 SiH/SiVi 0.7 1.2 1.5 1.0 1.0 1.01.0 1.0 1.0 (number ratio) Storage elastic 1,160 6,460 9,110 8,770 7,0808,620 7,460 960 860 modulus G′ after 3,000 sec) Storage elastic 10,69065,710 97,300 69,310 65,190 68,400 62,880 11,590 9,720 modulus G′ after7,200 sec) Time required for 1,870 1,420 839 1,010 830 1,050 810 1,9601,800 storage elastic modulus to exceed loss elastic modulus (sec)Viscosity 9.9 8.0 7.5 8.8 9.1 19.4 20.3 9.2 9.8 (Pa · s) Heatconductivity 2.0 1.9 1.8 1.9 2.0 2.5 2.5 2.0 2.0 (W/m · ° C.) Thicknessof 34 42 50 41 40 52 52 36 34 silicone composition after crushabilitytest (μm) Result of 0.83 0.66 0.54 0.69 0.70 0.51 0.50 0.80 0.84spreadability test (area covered with silicone composition/area ofsilicon wafer)

TABLE 3 Comparative Comparative Comparative Comparative ComparativeComparative example 1 example 2 example 3 example 4 example 5 example 6A-1 100 100 100 100 100 A-2 100 B-1 1900 1900 814 814 814 814 B-2 233233 100 100 100 100 Total amount of 2133 2133 914 914 914 914 filler C-17.9 7.4 3.2 3.2 C-2 4.7 C-3 4.6 D-1 0.06 0.06 0.06 0.06 0.06 0.06 E-1100 100 100 100 100 100 F-1 0.4 0.4 0.4 0.4 0.4 0.4 SiH/SiVi 1.0 1.0 0.40.4 0.4 0.4 (number ratio) Storage elastic Not Not Not cured Not curedNot cured Not cured modulus G′ becoming becoming (after 3,000 greasegrease sec) form form Storage elastic modulus G′ (after 7,200 sec) Timerequired for storage elastic modulus to exceed loss elastic modulus(sec) Viscosity (Pa · s) Heat conductivity (W/m · ° C.) Thickness ofsilicone composition after crushability test (μm) Result ofspreadability test (area covered with silicone composition/area ofsilicon wafer)

TABLE 4 Compara- Compara- Compara- Compara- Compara- Compara- Compara-Compara- tive tive tive tive tive tive tive tive example example exampleexample example example example example 7 8 9 10 11 12 13 14 A-1 100 300100 100 100 100 A-2 100 100 B-1 814 814 814 814 814 814 814 814 B-2 100100 100 100 100 100 100 100 Total amount of 914 914 914 914 914 914 914914 filler C-1 16.0 19.8 7.9 7.9 C-2 23.4 29.3 7.4 7.4 C-3 D-1 0.06 0.060.06 0.06 0.06 0.06 0.06 0.06 E-1 100 100 100 100 250 250 100 100 F-10.4 0.4 0.4 0.4 0.4 0.4 1.5 1.5 SiH/SiVi 2.0 2.5 2.0 2.5 1.0 1.0 1.0 1.0(number ratio Storage elastic 217,930 336,180 149,030 261,350 Not NotNot Not modulus G′ cured cured cured cured (after 3,000 sec) Storageelastic 305,810 477,060 232,690 347,550 modulus G′ (after 7,200 sec)Time required for 620 630 770 690 storage elastic modulus to exceed losselastic modulus (sec) Viscosity 8.6 8.0 7.7 7.4 (Pa · s) Heatconductivity 1.9 1.9 1.8 1.7 (W/m · ° C.) Thickness of 94 96 90 91silicone composition after crushability test (μm) Result of 0.30 0.260.33 0.32 spreadability test (area covered with siliconecomposition/area of silicon wafer)

From the results of Tables 1 to 4, Examples 1 to 18 satisfying therequirements of the present invention showed smaller thicknesses of thesilicone composition after the crushability test and larger resultingvalues of the spreadability test, compared with Comparative examples 1to 14. Accordingly, it could be confirmed that the silicone compositionof the present invention enables the heat-dissipating grease to becompressed into a prescribed thickness when the composition is used asthe heat-dissipating grease to be placed between a heat-generatingmember and a cooling member, and also enables the appliedheat-dissipating grease to sufficiently spread over the wholeheat-generating part.

That is, in the method for manufacturing a heat-conductive siliconecomposition, a heat-conductive silicone composition excellent incrushability and spreadability can be surely obtained by selecting, fromthe produced silicone compositions, only compositions that can provide acured product in which the storage elastic modulus G′ after 3,000seconds from the start of holding is 10,000 Pa or less, the storageelastic modulus G′ after 7,200 seconds from the start of holding is100,000 Pa or less, and the storage elastic modulus G′ exceeds the losselastic modulus G″ after 800 seconds or more from the start of holdingwhen the storage elastic modulus G′ and the loss elastic modulus G″ ofthe silicone composition is measured by the above-mentionedviscoelasticity measurement apparatus under the above heat increaseconditions and high-temperature holding condition.

It is to be noted that the present invention is not limited to theforegoing embodiment. The embodiment is just an exemplification, and anyexamples that have substantially the same feature and demonstrate thesame functions and effects as those in the technical concept describedin claims of the present invention are included in the technical scopeof the present invention.

The invention claimed is:
 1. A silicone composition comprising: (A) 100parts by mass of an organopolysiloxane having at least two aliphaticunsaturated hydrocarbon groups per molecule, and having a kinematicviscosity at 25° C. of 60 to 100,000 mm²/s; (B) 100 to 2,000 parts bymass of a filler containing an aluminum powder and a zinc oxide powder;(C) an organohydrogenpolysiloxane having two or more silicon-bondedhydrogen atoms (i.e. SiH group) per molecule, in such an amount that aratio of a number of the SiH groups in the component (C) to a totalnumber of the aliphatic unsaturated hydrocarbon groups in the component(A) ranges from 0.5 to 1.5; (D) a platinum group metal catalyst in anamount of 0.1 to 500 ppm in terms of platinum with respect to thecomponent (A); (E) 1 to 200 parts by mass of a hydrolyticmethylpolysiloxane represented by the general formula (1), based on 100parts by mass of the component (A),

wherein R¹ represents an alkyl group having 1 to 6 carbon atoms and “a”is an integer of 5 to 100; and (F) 0.05 to 0.4 parts by mass of one ormore retarders selected from the group consisting of acetylenecompounds, nitrogen compounds, organophosphorous compounds, oximecompounds, and organochlorine compounds, based on 100 parts by mass ofthe component (A); wherein when a storage elastic modulus G′ and a losselastic modulus G″ of the silicone composition is measured, by means ofa viscoelasticity measurement apparatus capable of measuring shearmodulus, while holding the silicone composition at 150° C. for 7,200seconds after the silicone composition is heated from 25° C. to 125° C.at a temperature increase rate of 10° C./min, from 125° C. to 145° C. ata temperature increase rate of 2° C./rain, and from 145° C. to 150° C.at a temperature increase rate of 0.5° C./min, the silicone compositioncan provide a cured product in which the storage elastic modulus G′after 3,000 seconds from the start of holding is 10,000 Pa or less, thestorage elastic modulus G′ after 7,200 seconds from the start of holdingis 100,000 Pa or less, and the storage elastic modulus G′ exceeds theloss elastic modulus G′ after 800 seconds or more from the start ofholding.
 2. The silicone composition according to claim 1, wherein thealuminum powder of component (B) includes an aluminum powder having anaverage particle size of 10 to 100 μm, and an aluminum powder having anaverage particle size of 0.1 μm to 5 μm.
 3. A heat-dissipating greaseobtained by curing the silicone composition according to claim
 1. 4. Aheat-dissipating grease obtained by curing the silicone compositionaccording to claim 2.